In the concrete batching industry, disposal of excess concrete, waste concrete and the washing of mixer trucks and plants create an environmental concern, and is a costly one.
Settling ponds have been traditionally used to separate solids from liquids. Solid laden slurry water to be disposed is discharged into a first pond for initial separation. At a second pond, further residual materials settle out, leaving clarified water to be transferred to a third pond. This system allows heavier material to be separated through gravitational settling. These solids are then eventually physically removed. However, for effective settling to occur, large settling ponds are required. This is undesirable in land scarce areas, for example, Singapore.
It is now desired to separate one or more solids from one or more liquids where beforehand, each solid existed in suspension in each liquid, in the form of fines, or settled in the liquid, in the form of silt, granite and sand. The purpose of separation is the recovery of either the solids or the liquids or both for further processing or for the release of one or the other into the environment.
A number of devices have been invented for separating solid laden slurry water and particles of varying size into distinct, separate groups. Screens have been widely employed for this purpose.
Static screens have often been used, where it provides a liquid reservoir at the top, a weir over which liquid flows, and a sloped screen which allows filtered liquid to flow through while the suspended solids are being separated. The solids then fall off the lower end of the screen. Static screens, while allowing continuous screening, handle only relative low flow rates and thus a large screening area is required to handle large flow rates. Furthermore, since the screen must slope downwardly and because a relatively long length of screen is required for effective separation, the head of suspension required at the top of the screen is relatively large. Further, such reclaimers may also allow too much product into the screens, as there is no way to regulate the flow of the product through the static screens.
Rotary screens, comprising a hollow rotatable drum having a perforated screening wall and having means for the delivery of the suspension to the interior of the drum, are an improvement over static screens by virtue of the rotation. This rotation continually presents a fresh screening surface to the suspension, thus allowing larger flow rates to be handled than with static screens. However, this type of screening, depending on the size of the solids, can either pass through the perforations with the liquid, or clog the perforations.
Another type of separator is the screw type reclaimer. These reclaimers employ a screw type conveyor for advancing the product through a reclaimer cylinder or chamber. The screw reclaimers are required to extend along the entire length of the reclaimer cylinder. Screw type conveyor reclaimers are inefficient because they work against the force of gravity. Screw conveyors force the product up and through the reclaimer cylinder or chambers instead of allowing the force of gravity to efficiently move the product therethrough. Further, these types of reclaimers provide limited hydraulic capacity in that they are unable to take multiple truckloads of solid laden slurry water.
A further method of separating waste aggregates from liquids involves the use of buckets on screws. Aggregate is introduced into the buckets, by way of the rotating screw, and the aggregate is advanced away from the liquid, thus separating it. This type of system is also inefficient in that the rotating screw needs to take into account the weight of the individual buckets on the screws.
Besides mechanical means, polymer or chemical addition systems have also been introduced to improve the removal of solids. For example, coagulants and flocculants are added to ease removal of suspended solids from the slurry water. However, the addition of these chemicals and additives may alter the quality of the reclaimed material and liquids, and hence, is also undesirable.
It is an object of the present invention to overcome or at least ameliorate one or more of the above problems in the prior art.
Discussion of any one of the prior art mentioned above is not to be taken as an admission of the state of common general knowledge of the skilled addressee.